I am encountering this error, too. Like some others, it seems to happen when I switch to another running program on my computer. When I switch back to RM, the error is there. It just happened on the Family view for me when I switched back from using Safari.
I am running 10.9.4 on my MacBook Pro. No, I'm not using the same RM database on my Mac and on my copy of RM in Parallels. RM is not even running on Parallels, which is, in fact, not running at all (Parallels).